Segmented polyester-urethane polymers wherein two dissimilar diol moieties are linked via reaction with a diisocyanate are known. For example, U.S. Pat. No. 2,880,192, Iwakura et al, J. App. Polymer Sci., V, 108-115 (1961) and U.S. Pat. No. 3,553,172.
When the glass transition temperatures of the two diol moieties of the polymer are different, i.e., one is substantially above ambient temperature and the other is below ambient temperature, the polymer is elastoplastic. The aforesaid elastoplastic polyurethanes are generally prepared in batch processes in solution using a high boiling solvent. The solvent process suppresses ester interchange but is undesirable from the industrial standpoint because of the long reaction times and because of the ecological problems associated with organic solvents and the energy required to remove the solvent from the polymer. Melt processes wherein the reaction is carried out in the absence of solvent have not gained acceptance because moderately low reaction temperatures are required to avoid randomization of the copolymer due to the ester interchange reaction which occurs between polyesters at elevated temperature. A process has now been discovered for making segmented polyester-urethane block polymers without using organic solvents which process minimizes randomization resulting from ester interchange. Moreover, certain polymers made by the new process exhibit improved properties compared to polymers of similar compositions prepared in an inert solvent.